Method and device for treatment of fibrous material

ABSTRACT

Methods and apparatus are disclosed for refining lignocellulosic material between a pair of relatively rotary refining elements forming an annular outer refining zone and a central feed zone. The method includes feeding the lignocellulosic material to the central feed zone, accelerating the lignocellulosic material through the central feed zone towards the annular outer refining zone without lignocellulosic material build up in the central feed zone and substantially without working the lignocellulosic material in the central feed zone, the density of the lignocellulosic material in the central feed zone being a maximum of about 10 kg/m 3 , and mechanically working the lignocellulosic material in the annular outer refining zone, and in which the relatively rotary refining elements have a relative speed of greater than about 50 m/sec.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for treatinglignocellulosic fibrous material in a refiner with opposed refiningmeans rotating relative to each other, one of which is stationary andone rotary, and which are preferably provided with refining elements,which form a refining gap with a refining zone for working the materialtherebetween. The present invention also relates to such method andapparatus in which the material is supplied to a feed zone locatedradially inside the refining zone. The present invention also relates toa feeding device for the lignocellulosic material.

The present invention more particularly relates to the manufacture ofvarious types of mechanical pulps, such as refiner mechanical pulp(RMP), thermomechanical pulp (TMP), chemi-mechanical pulp (CMP) andchemi-thermo-mechanical pulp (CTMP). The starting material in accordancewith the present invention can be wood chips, one-year plants as wheat,straw, bagasse or more or less worked pulp.

BACKGROUND OF THE INVENTION

The working of fibrous material in the known refiners most often iscarried out in an ineffective manner. A significant portion of theenergy input to these refiners is used for transporting the fibrousmaterial through the refiner, wherein friction and heat losses occurwhich do not result in the alterations of the fibrous material which arerequired for developing the pulp quality and for making the refiningprocess effective. It is therefore apparent that the energy consumptionis higher than that required for achieving the desired mechanicalworking; i.e., the desired pulp quality.

SUMMARY OF THE INVENTION

In accordance with the present invention, this and other problems havenow been solved by the discovery of a method for refininglignocellulosic material between a pair of relatively rotary refiningelements forming an annular outer refining zone and a central feed zonetherebetween, the method including feeding the lignocellulosic materialto the central feed zone, accelerating the lignocellulosic materialthrough the central feed zone towards the annular outer refining zonewithout lignocellulosic material build up in the central feed zone andsubstantially without working the lignocellulosic material in thecentral feed zone, the density of the lignocellulosic material in thecentral feed zone being a maximum of about 10 kg/m³, and mechanicallyworking the lignocellulosic material in the annular outer refining zonewherein the relatively rotary refining elements have a relative speed ofgreater than about 50 m/sec. Preferably, the density of thelignocellulosic material in the central feed zone is a maximum of about1 kg/m³.

In accordance with the present invention, apparatus has also beendiscovered for feeding lignocellulosic material to a refiner including apair of relatively rotary refining members including a correspondingpair of refining elements forming a refining gap and comprising anannular outer refining zone, and a central feed zone therebetween, acentral feed conduit having a predetermined diameter for feeding thelignocellulosic material to the refiner, the apparatus including a feedmember for mounting in the central feed zone in front of the centralfeed conduit, the feed member including a front axial screw and at leastone substantially radial rear wing displaced rearwardly from the frontaxial screw, the front axial screw having a diameter substantiallycorresponding to the predetermined diameter, and the at least one rearwing adapted to extend into the refining gap substantially to theannular outer refining zone. Preferably, the pair of relatively rotaryrefining members includes a stationary refining member and a rotaryrefining member, the central feed conduit being disposed in thestationary refining member and the feed member being disposed on therotary refining member. In a preferred embodiment, the apparatusincludes between about 2 and 4 of the substantially radial rear wingmembers.

In accordance with oen embodiment of the appartus of the presentinvention, the at least one rear wing member includes an outer end whichis curved from the intended direction of rotation of the rotary refiningmember.

The present invention offers a solution to the above problems, in thatthe residence time of the material in the feed zone is shortened, andsubstantially without mechanical working the cellulosic material passesthrough the feed zone to the radially outer refining zone. The residencetime should be less than about 2.5 sec, preferably less than about 1sec.

By means of a central feeding device the cellulosic material is fed inand accelerated outward without material build-up in the feed zone. Inthis manner, the material density in the feed zone is restricted to amaximum of about 10 kg/m³, and preferably to a maximum of about 1 kg/m³.In this way, contact of the material with the refining means in the feedzone is reduced, and thus the energy consumption in the form offrictional heat is reduced. Any proper mechanical working does not takeplace in the feed zone, and the energy consumption in this zonepreferably should be less than about 5% of the total energy consumption.

Instead, the energy input is transferred to the refining zone, where therelative speed between the refining elements is now quite high, andpreferably exceeds about 50 m/sec even in the inner portion of therefining zone.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail in the followingdetailed description, which, in turn, refers to the accompanyingdrawings, in which

FIG. 1 is a side, elevational, cross-sectional view through a refinerfor treating fibrous material according to the present invention;

FIG. 2 is a side, perspective view of a feed device according to thepresent invention;

FIG. 3 is a diagram comparing experiments in which the freeness is setforth as a function of the energy consumption.

DETAILED DESCRIPTION

The refiner shown in FIG. 1 comprises a refiner housing 10, in which astationary refining means 11 and an opposed rotary refiner means 12attached on a rotary shaft 13 are provided. The refining means, 11 and12, are provided with refining elements, 14 and 15, respectively, whichbetween them form a refining zone 16 in a refining gap 17. The refininggap 17 includes an inwardly located feed zone 18. The stationaryrefining means 11 is formed with a central feed opening 19 for thematerial which is to be worked. A screw feeder 20 for the material isconnected to the feed opening 19. The refiner housing 10 is providedwith an outlet 21 for the material passing through the refining gap,where the material is worked into the form of a pulp.

A central feeding device 22 is located on the rotary refining means, andit is formed with a front axial screw 23 and at least one substantiallyradial rear wing 24 on a rear wall 25 of the central feeding device 22.The diameter of the axial screw 23 corresponds to the diameter of thefeed opening 19. The rear wing or wings 24 extend into the refining gap17 through the feed zone 18 out to the refining zone 16.

The feeding device 22 can be formed with an axial screw 23 and wings 24either as one unit or as separate parts, which are attached individuallyto the rotary refining means 12.

The number of wings 24 is preferably 2 to 4, and they can be radial orformed with their radially outer ends curved from the rotation directionof the device.

The material to be treated is advanced to the refiner by means of thescrew feeder 20. The design of the feeding device 22 with a front axialscrew 23 ensures the transfer of the material from the screw feeder 20to the refiner, since the material is prevented from rebounding out intothe screw feeder 20. The presence of the rear wing or wings 24 alsocauses the material, which is fed by the axial screw 23 between therefining means, 11 and 12, to pass rapidly through the feed zone 18 tothe radially outwardly located refining zone 16 where the working of thematerial into the form of a pulp takes place. The wings 24 thusaccelerate the material outwardly without material build-up in the feedzone 18, in view of the fact that the material is locked up in a space,which is initially defined by the axial screw 23 and thereafter by therear wall 25 of the feed device 22, an opposed substantially smoothportion on the stationary refining means 11 and wings 24. The materialthus enclosed is subjected to an increasing centrifugal force, whichthrows the material outwardly to the refining zone. The material densityin the feed zone 18 can thereby be restricted to a maximum of about 10kg/m³, preferably a maximum of about 1 kg/m³. The contact of thematerial with the refining means in the feed zone, and the energyconsumption in the form of frictional heat is thereby reduced. No propermechanical working, thus, takes place in the feed zone 18, but it takesplace in the refining zone 16. The energy consumption in the feed zoneis preferably less than about 5% of the total energy consumption.

In the refining zone 16, where substantially the entire energy inputoccurs, the relative speed between the refining elements, 14 and 15,must be high, and preferably exceeds about 50 m/sec already in the innerportion of the refining zone.

EXAMPLE

A refiner of the type shown in FIG. 1 was operated partially with aconventional feeding device and partially with a feeding deviceaccording to the present invention for the manufacture of tissue pulp.The results are set forth in the following Table.

Regarding the load on the screw feeder 20, it was observed that it wasabout 40% lower with the feeding device according to the presentinvention, which indicates that this feeding device effectively draws inthe material into the refiner and moves it out to the refining zone.

TABLE CONVENTIONAL FEED ACCORDING TO FEED THE INVENTION Production ton/7.2 7.2 7.2 7.7 7.7 7.7 hour Spec. energy 1417 1333 1250 1013 974 974kWh/hour CSF ml 469 542 612 514 574 596 Tensile index 15.6 17.3 15.319.0 16.5 16.1 kNm/kg Tear index 5.87 6.48 5.68 6.22 6.17 6.27 Nm²/kg

It can therefore be seen that the quality of the produced pulp wassubstantially equivalent according to both of these alternatives.

The specific energy consumption, however, was reduced considerably byusing the feeding device according to the present invention.

For a corresponding freeness value, a reduction of the energyconsumption by about 25% was observed. See FIG. 3.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

What is claimed is:
 1. A method for refining lignocellulosic materialbetween a pair of relatively rotary refining elements forming an annularouter refining zone and a central feed zone therebetween, said methodincluding feeding said lignocellulosic material to said central feedzone at a first rate, accelerating said lignocellulosic material fromsaid central feed zone into said annular outer refining zone at a secondrate without lignocellulosic material build up in said central feed zoneand substantially without working said lignocellulosic material in saidcentral feed zone, the density of said lignocellulosic material in saidcentral feed zone being a maximum of about 10 kg/m³, said second ratebeing substantially greater than said first rate, and mechanicallyworking said lignocellulosic material in said annular outer refiningzone wherein said relatively rotary refining elements have a relativespeed of greater than about 50 m/sec.
 2. The method of claim 1 whereinsaid density of said lignocellulosic material in said central feed zoneis a maximum of about 1 kg/m³.
 3. Apparatus for feeding lignocellulosicmaterial to a refiner including a pair of relatively rotary refiningmembers including a corresponding pair of refining elements forming arefining gap and comprising an annular outer refining zone, and acentral feed zone therebetween, a central feed conduit having apredetermined diameter for feeding said lignocellulosic material to saidrefiner, said apparatus including a feed member for mounting in saidcentral feed zone in front of said central feed conduit for feedinglignocellulosic material at a first rate, said feed member including afront axial screw and at least one substantially radial rear wingdisplaced rearwardly from said front axial screw for feedinglignocellulosic material at a second rate, said front axial screw havinga diameter substantially corresponding to said predetermined diameter,and said at least one rear wing adapted to extend into said refining gapsubstantially to said annular outer refining zone.
 4. The apparatus ofclaim 3 wherein said pair of relatively rotary refining members includesa stationary refining member and a rotary refining member, said centralfeed conduit being disposed in said stationary refining member and saidfeed member being disposed on said rotary refining member.
 5. Theapparatus of claim 4 including between about 2 and 4 of saidsubstantially radial rear wing members.
 6. The apparatus of claim 4wherein said at least one rear wing member includes an outer end whichis curved from the intended direction of rotation of said rotaryrefining member.